I think the issue is that Liverpool players in the 70s/80s were pushed (Shankly, Paisley, Fagan) to work hard for the good of the team... including "flair" players like Dalglish. You also saw Ian Rush running his arse off to harass defenders.
Talent alone just wasn't enough and it's no coincidence that Liverpool won shed-loads in the 70s & 80s (including Souness who has a lot of league and Euro Cup medals). It wasn't just because they had excellent players, it was effort/team/mentality too.
In the same way, United won loads in the 90s/00s under Ferguson who (like the Liverpool managers) demanded max effort on top of ability. Beckham is a good example of talent and work ethic... if he lost the ball (like Pogba has done at times up the pitch), he raced back to try and tackle the player or cover.
I can't believe I'm part defending him but I think there's a small part of Souness who sees the talent of Pogba and thinks that with extra effort/better decisions, he'd be top, top class. He's probably also pissed that Pogba has more natural talent than Souness did but he doesn't have the same team/work/mentality mindset. In Souness's mind, maybe he thinks its a waste and that frustrates him.
Also, he was asked a specific question.
Again, can't believe I'm part defending Souness
but this is not a nobody, he was an excellent central midfielder so at least he's earned the right to comment. I don't think the time since he played makes a difference, the key attributes for a top player haven't changed, BUT I do see it as a bit of a crusade ... if he said it about other players (with similar issues), it'd come across as balanced but that's United for you... clickbait. Especially when there's no fecking football on!